1. Field of the Invention
The present invention relates to an electronic blackboard apparatus in which video information is depicted on a writing surface by means of a writing instrument and is simultaneously converted into electric signals by an electromagnetic converting means, the blackboard apparatus being capable of outputting an image similar to the video information on the basis of the electric signals.
2. Description of the Prior Art
Conventional apparatus of this type include one sort in which light is applied to a writing surface consisting of a windable sheet on which video information is written while the sheet is being wound up, the reflected light being detected by an image sensor or the like, and another sort in which a position-detecting section using matrix-like pressure-sensitive rubber is provided on the rear side of a writing surface which is made flexible so as to detect the writing pressure by means of detection voltage.
However, with such arrangements, measures must be taken to ensure that the winding-type sheet does not become deformed at the time of writing, and, in the case of the writing pressure type, a reinforcing structure must be adopted to provide strength sufficient to resist deformation due to the writing pressure. Consequently, the weight of the apparatus is necessarily large and the range of use of the writing surface is restricted. In addition, there has been a problem in that it becomes difficult to write on the writing surface because of repeated deformation of the writing surface due to external forces, and, hence, there has been a problem of limited durability.